Process for refining copper



Patented June 3, 1947 UNITED STATES PATENT OFFICE PROCESS FOR REFINI NG corrnn Hugh M. Shepard, Baltimore, Md., and James Howard Bryan, Roselle, N. J., assignors to American smelting and Refining Company, New York, N. Y., a corporation of New Jersey No Drawing. Application October 16, 1942, Serial No. 462,292

4 Claims. (cram-ins) This invention relates to the art of copper refining and more particularly to an improved process of making electrolytic copper. The present application is a continuation-impart of our prior patent application Serial No. 240,950, filed November 17, 1938.

The usual practice in refinin copper electrically by the so-called multiple process, comprises the steps of providing a relatively thin cathode starting sheet by depositing substantially pure copper onto the surface of a specially prepared blank, stripping the coated film of copper therefrom in the form of a sheet, flapping the sheet to remove kin-ks, then suspending the sheet .in

copper electrolyte solution and carrying out-elec- .trolysis using an anode formed of the impure .copper metal to be refined. During electrolysis the anode corrodes away and the copper constituent thereof enters the electrolyte solutionand is plated out on the cathodestarti-ng sheet, building it up to form a relatively thick sheet of electrolyticcopper.

'Flapping the sheets to removekinks and irregular areas, unavoidably formed in the sheets during the .stripping operation, is a tedious, labor consuming step which has been performed by hand,-as it was considered the only practical way of treating the sheets to straighten them. The sheets are supported either vertically or laid-horizontally-on a flat surface and the raised portions of the sheet beat down with a flap or paddle. Besides being a costly and labor consuming operation, hand fiapped starting sheets tend to warp and curl after a comparatively short time in the electrolytic bathQ To avoid serious trouble with short circuits, the practice has been to remove the starting sheets from the tanks at intervals and re-fiap them. Aside from these detrimental efiects it is practically impossible to effect uniformity from sheet to sheet by this method of treatment .Some attemps have been made, in the past, in an endeavor to improve the resistance of cathode starting sheets to distortion during electrolysis, for example, by corrugating the-sheets-to make them more rigid. This stiffens the starting sheet, but the change in surface contour results'in a lowering of the current efilciency.

It is the principal object of .this invention to eliminate hand flapping of thestrippedlcopper starting sheets, with its attendant disadvan ages, and provide an improved process of producing electrolytic copper whereby high current efficiencies are attained and an increased production rateafforded.

The invention is based primarily on the ,discovery that by subjecting the stripped thin copper starting sheets toa roller levellin treatment the kinks, warps and curlsare'ironed out and-deadflat sheets are produced which exhibit the prop.-

erty of .being self-straightening during the subsequent electrolytic refining operation. While once having conceived of this roller levelling treatment, it was expected that same would remove kinks, etc., it was entirely unexpected that this method-of treatment would result in producing a flat straight sheet exhibiting the improved characteristic property of self straightening during the subsequent electrolysis processing step. This self-straightening property is very beneficial, since in the usual copper refinery practice wherein the starting sheets are fiapped, it is necessary to withdraw the sheets one by one and straighten them during the early stages of the electrolysis. This reflapping was required because the initial copper deposit has a tendency to make the sheets curl :or warp, which, if not corrected, resulted in short circuits. By utilizin the novel method .of this invention for straightening the sheets, however. ;a marked improvement in current effi- ,ciency and lowering of labor costs is achieved.

To more particularly describe the method of producing electrolytic copper according to the improved process of this invention, the following specific example is given as being typical:

E trample Cathode starting sheets (approximating 1% inch thickness and 3' x 3' in dimension) were each made by electrolytically depositing copper, from a cOpper sulphate electrolyte solution, on a smooth copper blank, the surface of which had been previously coated with oil and graphite. After the copper deposit had been built up to the desired thickness, .it was stripped from the blank in the customarymanner providing a thin copper sheet. Then, instead of handrflapping the thin starting sheet, it was roller-levelled bypassing it between an upper and lower train of rolls which were chemicallynon-reactive with respect to the copperflsheet material. In this way, a dead-flat, self-straightening starting sheet was formed. The straightened sheets were then suitably suspended in the electrolytic tank and accurately spaced bctweenimpure copper anodes and electrolysiscarried out in the usual manner producing a relatively thick cathode sheet of electrolytic copper. as the finished product.

. -In utilizing our improved method of producing electrolytic copper, it has becnfound thatroller levelling rolls made of .iron or the like metal, which is more chemicallyactive than copper, cannot be usedsuccessiully for treating the ,copper sheet, inasmuch as displacement of the copper by the moreactive metal takes place under ordinary ,conditions,of treatment. Removal of copper from ,the starting sheet is very pronounced when ,plain steel rolls are used for processing coppersheets electro-tchemically deposited vfrom a 3 copper sulphate-sulphuric acid electrolyte solution.

Preferably the rolls or roll surfaces coming in contact with the copper starting sheet are made of high carbon chrome-nickel steel. A rustless steel containing from 0.9 to 1.1% carbon, 14 to 18% chromium and up to 0.5% nickel has been found to work very satisfactorily. Other suitable corrosion resistant ferrous and non-ferrous metal material which possesses sufl'icient durability may be employed for this purpose. The rolls are staggered and meshed slightly as is conventional in roller-leveling mechanism so that the sheet as it progresses therealong is flexed first one way and then the other whereby the sheet is straightened and made to lay perfectly flat without appreciably reducing its thickness or cold working the sheet to any considerable amount.

By roller-levelling the starting sheets, instead of hand flapping them, a substantially continuous and automatic process is provided by which the production of electrolytic copper is markedly speeded up. Moreover, the roller-levelling treatment performs the dual function of removing kinks, warps and surface irregularities to form a dead-flat sheet and of producing a starting sheet exhibiting the highly desirable property of being self straightening when slightly deformed and suspended in the electrolytic tank. Further, this characteristic property tends to prevent curling and distortion of the cathode starting sheets during electrolysis.

While certain specific disclosures have been made to more distinctly describe the invention, it will be understood that various changes in operating procedures may be made by those skilled in the art without departing from the spirit and scope of the invention as defined in the annexed claims.

What is claimed is:

l. The improvement in the method of producing electrolytic copper by the multiple system which comprises the steps of electrodepositing a relatively thin film of copper on the surface of a blank, stripping the copper deposit therefrom in the form of a sheet, thereafter subjecting said sheet to a roller-leveling treatment to remove kinks, warps and surface irregularities without appreciably reducing its thickness or cold working the sheet to any considerable amount, said roller-leveling treatment comprising passing the sheet between an upper and lower train of rolls which are chemically non-attacked by the copper sheet material being treated whereby a deadflat sheet is produced which exhibits the characteristic property of being self straightening during subsequent electrolysis, and employing said dead-flat, self-straightening sheet as a cathode in producing electrolytic copper.

2. In the art of producing electrolytic copper by the multiple system in a continuous automatic manner, the process comprising forming a cathode starting sheet which is self-straightening during subsequent electrolysis by electrolytically depositing copper on a blank surface from which it can be stripped, stripping the deposited copper therefrom in the form of a thin sheet, passing said thin stripped electrolptic copper sheet between roller-levelling rolls, which rolls are chemically non-attacked by electrolyte which may be retained on the surface of said thin copper sheet, to cause the kinks and irregular surface areas throughout the sheet to be ironed out and a straight, dead-flat copper sheet provided which is self-straightening during subsequent electrolysis, thereafter suspending said thin selfstraightening copper sheet as a cathode in an electrolytic cell containing copper electrolyte solution, and carrying out electrolysis with an anode of impure copper to cause the impure copper anode to corrode away and the copper constituent to enter th electrolyte and be deposited out on the cathode starting sheet thereby producing electrolytically refined copper.

3. The process for producing electrolytic copper by the multiple system characterized in that the copper is deposited from the electrolyte upon a starting sheet that is self-straightening in said electrolyte during electrolysis which comprises: forming a cathode starting sheet by electrolytically depositing copper from a copper sulphatesulphuric acid bath upon the surface of a blank from which said deposited copper can be removed as a thin sheet, stripping said thin copper deposited sheet therefrom, passing said sheet between coacting upper and lower trains of roller-levelling rolls, which rolls are chemically non-attacked by copper sulphate which may be retained on said stripped copper sheet to form a straight deadflat copper starting sheet which is self-straightening in the electrolyte during electrolysis, placing said dead-flat self-straightening sheet in the electrolyte and electrolytically connecting it as a cathode with an anode of impure copper, and carrying out electrolysis whereby impure copper from the anode is dissolved and electrolytically deposited out on said cathode starting sheet thereby producing electrolytic copper.

4. In the art of producing copper by the multiple system, electrolytic process wherein a thin electrodeposited copper starting sheet serves as the cathode upon which copper is electrolytically deposited from the electrolyte, that improvement which consists in flattening the starting sheet and imparting to it the property of being selfstraightening during the electro-deposition of copper thereon, by passing said starting sheet through roller-levelling rolls which are chemically non-reactive with the sheet, and thereafter utilizing theresulting flattened, self-straightening sheet as the cathode in conducting the electrolytic process.

HUGH M. SHEPARD.

JAMES HOWARD BRYAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 41,306 Lauth Jan. 19, 1864 1,163,337 Guggenheim Dec. 7, 1915 1,698,486 Yungblut Jan. 8, 1929 1,836,368 Eppensteiner et a1. Dec. 15, 1931 2,048,854 Dyer July 28, 1936 2,059,993 Hanson Nov. 3, 1936 202,027 Harvey Apr. 2, 1878 1,817,707 Rees Aug. 4, 1931 494,231 Schoemnehl Mar. 28, 1893 377,487 Hayden Feb. 7, 1888 OTHER REFERENCES The Making, Shaping and Treating of Steel, pages 1207-8, 5th edition, by Camp, 1940.

Electrometallurgy, by McMillan and Cooper, pages 275-289, 4th edition, 1923.

Electrochemistry, by Brockman, 1931, page 

